solutions/0079-Word-Search/0079.py

from typing import List

class Solution:
    def exist(self, board: List[List[str]], word: str) -> bool:
        if not board:
            return False
        
        for i in range(len(board)):
            for j in range(len(board[0])):
                if self.dfs(board, i, j, word):
                    return True
        return False

    def dfs(self, board, i, j, word):
        if len(word) == 0:
            return True
        if i < 0 or i >= len(board) or j < 0 or j >= len(board[0]) or word[0] != board[i][j]:
            return False
        tmp, board[i][j] = board[i][j], '#'  # '#': visited
        ans = self.dfs(board, i - 1, j, word[1:]) or self.dfs(board, i + 1, j, word[1:]) or self.dfs(board, i, j - 1, word[1:]) or self.dfs(board, i, j + 1, word[1:])
        board[i][j] = tmp  # recover board[i][j]
        return ans

if __name__ == "__main__":
    board = [["A","B","C","E"],["S","F","C","S"],["A","D","E","E"]]
    word = "ABCCED"
    print(Solution().exist(board, word))